None
Not applicable
1. Field of the Invention
This invention relates to methods and apparatus for suppressing explosions in gas lines, including natural gas lines and the like but specifically relating to gas lines carrying pyrophoric gases such as silane (SiH4).
2. Description of the Related Art
Silane (SiH4) is a pyrophoric gas used extensively in semiconductor manufacturing. When silane is exposed to even very small amounts of oxygen, the silane will burn extremely quickly, leaving behind a white powdery residue of xe2x80x9csand-likexe2x80x9d material (i.e., SiO2). In the normal course of semiconductor operations, silane lines are sometimes compromised through small leaks or cracks and exposed to oxygen. When this occurs, the resulting reaction burns through the silane line in both directions, leaving behind the powdery residue and rendering the line unusable. All lines and exposed equipment where this occurs require replacement, often at quite significant cost and effort. This occurs frequently enough that some facilities are known to install duplicate silane lines during construction for just these events. The present invention constitutes a method and apparatus intended to stop any such explosive reaction as soon as it encounters the apparatus, thus protecting all equipment on the side of the apparatus opposite the origin of the explosion.
The present invention provides a method and apparatus for first detecting and then terminating the occurrence of an explosion in a gas line, particularly as to an explosion of silane gas within a pipe line in the course of semiconductor chip fabrication. Silane (SiH4) is a pyrophoric gas, and must be contained within a pipe line that isolates the silane from the atmosphere. Upon any leakage of air into that pipe line, the silane can explode to yield disastrous results both to the particular operation and to the facilities as a whole, especially with respect to the wafer fabrication chambers within which the wafer is to be fabricated in part through use of the silane gas. The invention does not prevent an explosion, but rather limits the extent of damage that an explosion produces, and in particular xe2x80x9cdownstreamxe2x80x9d damage towards those fabrication chambers. The method and apparatus can also be used for the handling of other gases under similar circumstances.
Operation of the invention rests on event detection, on the immediate reduction of heat within an explosion by use of a filter medium, and then upon application of the initial pressure surge of the explosion to a multi-port diaphragm that both inhibits re-initiation of the explosion and protects the downstream portion of the gas line. The latter step is of particular importance in semiconductor fabrication, since that work requires an ultimately clean environment, and if contaminated by a silane explosion, a gas line becomes useless for that purpose and must be replaced.
The prior art in this field has been concerned with the suppression or limitation of damage of (a) explosions in enclosed spaces and (b) the prevention of flashback along a pipeline from an intended combustion source back to a source of combustible fuel. As will be shown below, none of the prior art of which the inventors are aware has considered downstream damage effects of pipeline explosions, or in particular the suppression of explosions of pyrophoric gases in a pipeline. Filter type media have been used to control small explosions such as exists in auto air bags. High purity diaphragm valves are used throughout the semiconductor business, but none in the manner of the present invention. Prior devices have been simply on/off devices manually or air actuated.
The control of fire has as long a human history as perhaps any other activity other than stone tool-making. In modern times, such activities center largely on apparatus, most often operated electrically, that first detect the presence of a fire and then release a fire suppressant in response thereto. Typical of such endeavors is the apparatus disclosed in U.S. Pat. No. 5,718,294 issued Feb. 17, 1998, to Billiard et al., together with U.S. Pat. No. 5,816,330 issued Oct. 6, 1998, to the same inventors, which treat a manually operated handle that initiates either an electrically responsive initiator or a gas-generating cartridge activator, these then acting to generate, e.g., the firing of a blasting cap, so as to rupture a disc to release fire suppressant to the area. Another device that employs such a rupture disc is found in U.S. Pat. No. 6,006,842 issued Dec. 28, 1999, to Stilwell et al.
Somewhat different types of fire detection and suppression apparatus are found in U.S. Pat. No. 5,826,664 issued Oct. 27, 1998, to Richardson, which discloses such a device mounted externally to a tank within which a fire or explosion is to be suppressed by injection of suppressant medium into the tank, and in U.S. Pat. No. 6,012,532 issued Jan. 11, 2000, to Kiefer et al., which discloses a flexible bladder containing an inert gas that upon rupture of the bladder will help suppress a fire or explosion.
U.S. Pat. No. 6,104,301 issued Aug. 15, 2000, to Golden, discloses a fire detection and suppression device that operates through an electronic processor to detect and respond also to other types of hazard, e.g., as an intrusion detector. A more extensive electronically operated fire detector and suppressor which employs several detection means and provides multi-level responses is described in U.S. Pat. No. 6,057,549 issued May 2, 2000, to Castleman. Although this ""549 patent to Castleman mentions the clean room environment as an example of one in which fires can occur, none of the aforementioned patents address fires or explosions that actually occur within a pipeline.
Further elaboration of the specific features that appear in these patents are found in U.S. Pat. No. 4,173,140 issued Nov. 6, 1979, to Liebman et al., which discloses a trigger device including a pressure sensor and at least two flame sensors, and which serves to erect an explosion barrier in front of an explosion to limit its extent; U.S. Pat. No. 5,225,622 issued Jul. 6, 1993, which discloses an acoustic shock wave attenuating assembly; U.S. Pat. No. 4,505,180 issued Mar. 19, 1985, to Hinrichs, which discloses a rupture disc assembly that does not burst under high pressure from one direction but bursts at a relatively low pressure from the opposite direction and is useable in the context of hand-held firearms; U.S. Pat. No. 4,579,315 issued Apr. 1, 1986 to Kowalski, which discloses a quick-opening valve for release of fire suppressant after having been activated by an electrical signal; U.S. Pat. No. 6,031,462 issued Feb. 29, 2000, to Van den Schoor et al., which discloses a rate-of-rise detector that monitors the pressure within a protected area and generates a signal to release fire suppressant when that pressure increases at more than a predetermined threshold rate; and U.S. Pat. No. 5,122,628 issued Jun. 16, 1992 to McClelland et al., which discloses a pressure increase detector for the like purpose.
Another body of patents specifically treats the occurrence of explosions in gas-containing pipe lines, but none of such patents of which the inventors are aware addresses the particular problem of pyrophoric materials. Thus, U.S. Pat. No. 5,103,916 issued Apr. 14, 1992, to McClelland, discloses a differential fire and explosion protection system for protection against explosions in pneumatic transport systems, often used with process equipment, that convey potentially combustible particulate materials such as dust. Two thermocouples, one fast-responding and the other slow-responding, are disposed within an air outlet duct, and the occurrence of a temperature differential between the two thermocouples, arising from an explosion, causes shut-down of the blower operating the transport system, and the resultant pressure drop, along with subsequent release of fire suppressant material, act to control the explosive condition.
U.S. Pat. No. 4,928,255 issued May 22, 1990, to Brennecke et al., describes a method and apparatus for explosion protection in pipelines and the like by monitoring chronologically successive values of the system pressure in a potentially explosive area and comparing the values obtained with a predetermined pressure threshold so as to enable initiation of explosion protection means, e.g., the release of extinguishing agents. The invention seeks greater accuracy and faster response in recognizing a dangerous condition by way of setting the pressure threshold on the basis of recently recorded pressure values.
U.S. Pat. No. 5,794,707 issued Aug. 18, 1998, to Alhamad, describes a passive flame arrestor disposed within a pipeline or conduit to prevent upstream backflashing (to the source of flammable material), and comprises a contained layer of nested spheroids formed from expanded metal sheets made from magnesium alloy foil.
U.S. Pat. No. 5,676,712 issued Oct. 14, 1997, to Anderson, describes an active flame arrestor system that includes monitoring a flow system through which is passing a stream of combustible gas, detecting by optical mean a deflagration event that produces a propagating flame front, and opposedly directing at such a flame front a pressurized non-flammable gas of sufficient volume and velocity to extinguish that flame front. The system is useable in clean rooms in which are manufactured integrated circuits, and that use may apply to production lines that employ pyrophoric gases such as silane. The present invention is distinguishable from Anderson, however, in that the latter does not address the problem of downstream gas line contamination from silane combustion.
Specifically, if a silane line is compromised by the entry of air, the silane burns as a flame that spreads from the source of air entry on through the line in both directions, and in the process the flame produces a sand-like residue that is deposited along the line that renders the line, and also the chambers within which the silane is intended for use, unuseable thereafter for integrated circuit manufacture. The Anderson device treats a flow system extending from a fuel source to a place of intentional fuel combustion, and the device is intended to prevent flashback from the point of combustion back to the fuel source. The device will extinguish such a flame, but in addressing only the prevention of flashback in the direction of the fuel source, Anderson provides no means for limiting the spread of such contaminating residue downstream from the combustion sourcexe2x80x94the flames sought to be controlled in the Anderson device and in the present invention are traveling in opposite directions.
Application of the Anderson method and apparatus in the context addressed by the present invention is further precluded by the means by which the Anderson device controls the undesired flame, namely, by sending towards such an approaching flame front (i.e., downstream towards the point of intended combustion) a quantity of non-combustible gas, the effect of which would necessarily include transmitting in that same direction some quantity of combustion products, i.e., in the case of a silane explosion the very sand-like contaminant that it is the purpose of the present invention to prevent from so traveling. Anderson thus teaches precisely away from the present invention.
Finally, U.S. Pat. No. 3,933,444 issued Jan. 20, 1976, to Kilgore, describes a flashback arrestor that likewise addresses the control of flame fronts that are traveling in the direction opposite to that which is of concern in the present invention. The Kilgore device comprises a valve at an inlet end of a gas line that is actuated by pressures from the flashback at the outlet end of the gas line, and including a piston that is forced by such back pressure into a valve seat at the inlet end of the gas line. That process leaves the gas line itself entirely contaminated with combustion products, hence the Kilgore device is inapplicable to the problem that the present invention addresses.
Silane is a gas that is critical in the manufacturing of integrated circuits (ICs), inasmuch as it provides the silicon for deposition on the IC. Every integrated circuit manufacturing facility in the world that treats silicon-based ICs has at least one source for this gas. FIG. 1 shows a typical flow path for silane, designated generally herein as system 10 (prior art). The general structure of system 10 may include a subfab floor 12, above that a waffle slab 14, and then above that a raised floor 16, on which the various active components of system 10 are installed as hereinafter shown and described.
Commencing at the level of subfab floor 12, silane gas bottles 18 are typically stored in a gas cabinet or, in more recent installations and as shown in FIG. 1, in an outside gas bunker or gas pad 20. The silane gas bottles 18 and associated valves 22 and gas line 24, both in such a gas cabinet, bunker or gas pad 20, are subject to being compromised through human error when handling the gas upon changing bottles 18, purging control panels, or replacing hardware on the gas panel (not shown) itself. One loose fitting or a wrongly opened valve 22 would allow exposure of the silane to the atmosphere, causing the pyrophoric silane reaction to begin.
From the cabinet or gas pad 20, the silane will typically flow through one or more valves 22 to line 24 and thence to a valve manifold box (xe2x80x9cVMBxe2x80x9d), of which VMB 26 is shown in FIG. 1. The purpose of VMB 26 is to provide gas distribution means whereby a particular gas can be routed from a single source of that gas for use in more than one tool. VMB 26 will typically have 2-8 branches (also called xe2x80x9csticksxe2x80x9d), of which only four sticks 28 are shown in FIG. 1 (and for which the subsequent routing is shown only for stick 28, each such stick 28 then carrying the silane from its source to a particular tool. Valves 22 of VMB 26 may be either automatically controlled or manual, but both offer opportunities for human error and component failure.
As to each stick 28, from VMB 26 the gas flows to gas isolation box (xe2x80x9cGIBxe2x80x9d) GIB 30, which contains a valve 22. GIB 30 is usually located near to the tool at which the gas is to be used, and gives to the tool technicians the ability either to view and regulate the gas pressure or to turn the gas off before it gets to the tool itself.
The next point along the path of system 10 is commonly referred to as a xe2x80x9cgas jungle,xe2x80x9d e.g., gas jungle 32, which may be either a part of the tool or more commonly a gas box outside of the tool. This is where all of the gases serving the tool come together before actually going into the individual chambers of the tool. Gas jungle 32 is the final point of pressure regulation as well as the point of flow control. This flow control is achieved by using a device called a mass flow controller, or xe2x80x9cMFC,xe2x80x9d e.g., MFC 34. Also included within gas jungle 32, but not shown for purposes of clarity, will be an array of valves, regulators, pressure transducers and the like, as will be known to a person of ordinary skill in the art. This part of the line is also subject to human error and possible silane reaction in the course of maintenance work. The box-like elements shown separately to the left of gas jungle 32 in FIG. 1 are an array of chambers within a particular tool to which system 10 is attached through gas jungle 32, and in this case showing four chambers 36 only as an example, since that number may vary in practice.
If a leak occurs at any point along the path just described, because of the resulting pyrophoric explosion the line will become worthless for production, from the point of the leak to the next closed valve. The cost of that damage can range from a few thousand dollars to a half million dollars, depending on the extent of the line exposure. This does not take into account downtime or opportunity costs. The inventors herein are unaware of any art prior device that is intended to address the specific problem just described. It is the purpose of the present invention to stop the reaction regardless of the direction of the leak from the apparatus comprising an embodiment of the invention, thus limiting the damage. The apparatus may, of course, be used at multiple points along a given line to achieve extra line protection.
The apparatus serves as a protection device for silane lines as used in the manufacture of semiconductor integrated circuits, but also, with proper scaling, can be used in other areas such as natural gas lines and the like. Basically, the apparatus acts as a flash arrestor, but by way of methods and apparatus not previously seen in the art. The apparatus is activated to close by means of a 2-seat flow/pressure system that operates in either direction; employs xe2x80x9coff-setxe2x80x9d filter media packing to extend reaction flow path; acts as a fire safety device, equipment protection device, double isolation valve, and a sub-micron filter; is compatible with traditional UHP components as well a surface mounts; comprises a passive component; serves also as a shock tube so as to concentrate the power of a shock wave and corresponding pressure increase that actuates the valve; and, so as to operate in either direction, employs UHP activators that are cross-connected so that the apparatus will activate from a stimuli that arrives from either xe2x80x9cupstreamxe2x80x9d or xe2x80x9cdownstream.xe2x80x9d The apparatus may be placed anywhere along silane or similar gas lines, typical installation locations for the apparatus as now contemplated by this present specification being shown by the dark circles in FIG. 1; and similarly in natural gas lines or other applications in the petroleum industry, in the realm of aerospace and rocketry, or in any other context wherein flammable, explosive, or pyrophoric substances present a hazard. Wherever placed, the apparatus is intended to stop the silane/oxygen or similar such reactions, thus preserving from damage all lines and equipment on the protected side of the apparatus, or otherwise preventing catastrophic disasters.
There are two basic processes at work in the apparatus. The first is the reduction of heat in the reaction, using a filter media to temporarily stop the reaction (on the order of milliseconds). The second process lies in using the shockwave and the momentary pressure surge of the reaction to actuate a multi-port diaphragm valve. This event occurs before the reaction has had any opportunity to restart, thus isolating the reaction and protecting the portion of the line isolated by the device on the opposite side of the reaction.
The device consists of two canisters containing both filter media and inert packing. The filter media prevents particulate contamination through the pipeline, while the packing removes enough heat from the reaction to stop the reaction and flame front momentarily. The canisters are attached to a main body that directs the flow path of the gases. The flow path for the reacted gases is intentionally designed such as to delay the flame front in order to provide adequate time for the valves to shut once actuated by the shock wave and actuation pressure. This process isolates the contaminated line from the uncontaminated portion of the line. There are two valve seats with diaphragms that all close initially under pressure of the shockwave, then remain closed via the use of magnetic forces.
The apparatus also acts as a double isolation valve. Both valves (one in each canister) are positively operational manually in the On and Off positions. The Armed position is used to activate the passive silane arrestor, during which the valves are held open magnetically, and held magnetically closed if activated.